1. Field of Invention
This invention relates examining the human body with X-ray by means of computed tomography, and more specifically, to a tomography apparatus that allows a patient to be scanned with his torso upright.
2. Description of the Prior Art
X-ray computed tomography is one of the most frequently utilized modalities in diagnostic imaging. Recent developments in multi-slice CT technology have proven the diagnostic value of CT in areas such as cardiology. Since cardiovascular disease is currently the leading cause of death in the United States, it is desirable that cardiac CT scanners become a routine examination tool just as X-ray examinations have become, capable of being utilized in small hospitals, outpatient clinics, and doctors' offices. This requires a new generation of CT scanners that are more affordable, convenient to use, and able to detect minute abnormalities for early diagnosis.
In current commercially available multi-slice CT scanners, a patient must be laid on a bed. This is not the optimal position for to examine for cardiovascular diseases because when a patient is lying down, his organs take more relaxed positions and thus it becomes more difficult to detect minute abnormalities. In addition, eliminating the patient bed can reduce the overall cost of the machine. Therefore, an upright CT scanner is more suitable in cardiology. However, it is not possible to eliminate the bed for conventional CT scanners. This is because the bed translation, combined with the gantry rotation, forms a spiral trajectory, which is the foundation for the current narrow CT detector to continuously scan a section of body. In 1979, Richard T. Bemardi patented a hybrid scanner that scans in either vertical or horizontal positions in his U.S. Pat. No. 4,316,091. Practically, however, his design has safety concerns and is probably more expensive than conventional CT scanners.
With the advent of the digital X-ray detector, the use of 2D silicon detectors for CT scanners has been the subject of intensive research. Since one view of a 2D digital X-ray detector can cover the entire heart, the spiral motion of the conventional CT scanner is no longer necessary. One successful example is C-arm based CT, where an X-ray tube and a 2D digital X-ray detector are mounted at two ends of a C-arm. Despite many advantages of C-arm CT scanner, structural instability of C-arm during the oscillating rotation causes the problem of image registration. In addition, C-arm CT scanners may not be able to scan a large patient or part of body that is far from the axis of rotation center without a large, expensive detector.